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Central air conditioning

Central air conditioning buying guide

Last updated: May 2014
Getting started

Getting started

When you install central air conditioning size matters. Underestimate your cooling needs, and you could be sweating. Buy more power than you need and your living space may become cold and clammy. Any contractor you hire should calculate the size of the cooling equipment you need by using such recognized methods as the Air Conditioning Contractors of America (ACCA) Manual J. If you already have ductwork for your heating, adding a central system can cost less. But keep in mind that ducts used for heating might not be the right size or in the right location for optimal cooling.

Your contractor should use a duct-sizing method such as the ACCA Manual D. The pros should make sure that all duct sections are properly sized and that there are enough supply registers to deliver sufficient air to the right spots. Not only is the proper size ductwork essential for meeting each room's cooling needs but also because undersized ductwork can make for noisy operation. Leaky or uninsulated ducts can reduce system efficiency considerably. All joints and seams must be sealed--and not with duct tape that can dry and fall off.

If your home doesn't have ducts, adding them can be expensive, though if you plan to cool your entire home, central air is typically the best choice. If you are not planning to cool the entire home, you might want to consider a split-ductless system. Unlike central systems, split-ductless systems need no ductwork (though they require connections for electrical, refrigerant and condensate drains), making them easier to add to homes with designs that aren't conducive to installing ductwork.

The most and least reliable

While Consumer Reports would like to provide you with brand and model ratings of central air-conditioning systems, it would not be practical because there are so many variables to consider, including a home's size and design, and how the air-conditioning unit is installed. In fact, a significant variable affecting performance is the quality and construction of the duct distribution system. Poorly designed or installed ductwork can cause improper cooling, noise and even equipment failure. Instead, to help you make an informed choice we surveyed almost 34,000 readers who bought systems from 2007 through 2013 to find out which brands were most and least reliable

.

Types

The most common type of central air conditioning is the split system which features a condenser outside the home and fan-and-coil system inside connected by pipes carrying refrigerant. However, not every home can accommodate the ductwork needed to install central air. For such residences, a split ductless system is an option.

Central air conditioning

Central air-conditioning systems use ducts to distribute cooled air throughout the house. In a "split system," the typical design, refrigerant circulates between an indoor coil and a matching outdoor condenser with compressor. The refrigerant cools the air, dehumidifying it in the process; a blower circulates air through ducts throughout the house. A variation is the "heat pump," a type of system that functions as heater and cooler. When used as an air conditioner, a heat pump discharges heat from the house either into the air or deep into the ground. In the winter, a heat pump extracts heat from the ground or the air to warm the house.

Split ductless systems

Split ductless systems are similar to central air. They have an outside condenser and one to four indoor units with blowers mounted high on the wall. Tubing connects the parts and circulates refrigerant. The tubing, along with an electric and drain line, is run through a 3-inch hole hidden behind the indoor unit. Each indoor unit cools the room it's installed in and has its own remote control. Unlike central systems, split ductless systems need no ductwork, making them easier to add to homes without existing ducts. Split ductless systems are more expensive than window air conditioners, and professional installation is recommended, but it's a way to add cooling without tearing up walls to install ducts.

Pipes

Some systems use pipes instead of ducts, which distribute chilled water to heat exchangers in more than one room.

Features


When considering central air conditioning features, think about the size, design and efficiency of the unit.

Design

In a "split system," the typical design, refrigerant circulates between an indoor fan-and-coil and a matching outdoor condenser with compressor. The refrigerant cools the air, dehumidifying it in the process; a blower circulates air through ducts throughout the house.

A variation is the "heat pump," a type of system that functions as heater and cooler. When used as an air conditioner, a heat pump discharges heat from the house either into the air or deep into the ground. In the winter, a heat pump extracts heat from the ground or the air to warm the house.

Efficiency

This describes how much cooling the unit delivers for each watt of electricity. Efficiency is expressed as the Seasonal Energy Efficiency Rating, or SEER. The minimum SEER for a split system central air conditioner is 13.

Size

A synonym for the air conditioner's cooling capacity, size is measured in British thermal units per hour (Btu/hr.) or in "tons." One ton of cooling equals 12,000 Btu/hr.

Installation

What's the best way to ensure that the central air-conditioning system you choose is installed properly, and will provide the most efficient and reliable cooling for your home?

The pointers below can help you to find the right hardware and the right technician to install your system, whether you're replacing an older air conditioner or installing one for the first time.

Get the right contractor

Finding a trustworthy contractor to install and service an air-conditioning system matters the most. Here's what to do.

Ask around. Seek referrals from neighbors, family, or business associates. It's wise to get price quotes from at least three contractors.

Check the background. Contractors who bid on your installation should show you verification of bonding and insurance, plus any required contractor's licenses. Check with your local Better Business Bureau and consumer affairs office for complaint records. It's a plus if technicians are certified by a trade organization, such as North American Technician Excellence or HVAC Excellence, to service residential heating and cooling equipment. Those and other similar programs assess the technician's knowledge of specific types of equipment and their proper service methods. We believe that a contractor who has made the effort to be certified and has practiced this trade and learned from several years of service and installation experience will be a better service provider.

Get specifics. Contractors who bid on your job should calculate required cooling capacity by using a recognized method such as the ACCA's Residential Load Calculation Manual, also called Manual J. An additional reference for assessing ductwork needs is Manual D. The calculations produce a detailed, room-by-room analysis of cooling needs. Ask for a printout of all calculations and assumptions, including ductwork design. Be leery of a contractor who bases estimates merely on house size or vague rules of thumb.

Maintenance

A service plan that combines regular inspections with discounts on repairs and a labor warranty is worth negotiating into the overall price. Prices for such service vary widely. Follow these maintenance tips.

Call in a pro

Have a licensed professional perform important maintenance tasks, including changing all filters, cleaning and flushing the coils, draining the pan and drainage system, and vacuuming the blower compartments. The contractor should also check that the system is properly charged with refrigerant, that there are no leaks, and that all mechanical components are working properly. As with a room air conditioner, replace disposable filters regularly. Check them monthly and replace if dust and debris have completely coated the filter.

Insulate ductwork

Ensure that ducts throughout the system are sealed and insulated--up to 30 to 40 percent of your cooling (and heating) energy can be lost through leaks or when uninsulated ducts pass through uncooled spaces such as attics and garages.

Perform seasonal checks

During the season, keep vegetation at least two feet away from the unit. Clean the grills and filters monthly and replace the filters as needed. Clear debris and dirt from condenser coils and check for blockages in the pipe that drains condensed water from the indoor unit.

Use a programmable thermostat

Proper use of a programmable thermostat can reduce your cooling costs by up to 20 percent. Also consider adding a ceiling fan, which will allow you to set your thermostat to a higher temperature.

Upgrading

If you're upgrading your central air, don't automatically buy the same-sized system. Any changes you've made to improve your home's energy efficiency, such as replacing windows or adding insulation, can reduce your cooling needs. On the other hand, if you've added rooms, you might need more cooling. So have your contractor do a load calculation based on a recognized method, such as Manual J from the ACCA. The contractor's evaluation should include whether your ducts need to be resized, sealed and insulated, or replaced. Remember that an indoor evaporator coil and outdoor condenser must be a matched set, or the performance, efficiency, and capacity claims might not be accurate.

New systems are 20 to 40 percent more efficient than minimum-efficiency models made even 10 years ago. If you're replacing an old central-air system, you can expect to pay a few thousand dollars for the cooling equipment with a capacity of about three tons (36,000 Btu/hr.). If you need ductwork installed because you're starting completely from scratch or are upgrading a forced-air heating system, expect to pay double that. Of course, the cost depends on the size and configuration of your home. Improving the system's air-filtration capabilities is also easiest to do as part of a general upgrade.

Here are some factors that may affect the reliability of your system.

Matching new equipment with old

If you replace only the condenser, you have a "field matched" system that can be less efficient than advertised and that may require more repairs because of undetected incompatibilities between the indoor coil and the condenser.

Damper-zoned cooling

A large or multistory house is often divided into several heating and cooling zones to improve temperature control. But this type of system is complex and has many more moving parts and controls and so may require more repairs.

   

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